1. Field of the Invention
The present invention relates to detoxifying treatment for ballast water loaded to a ballast tank of a ship.
2. Description of the Related Art
These days, it comes under close scrutiny that vast amount of ballast water the water loaded into a ship and drained at each way port for keeping the ship steady) scattered all over the world destroys the gulf ecosystem of each way port, because of expansion of trades and global operation of large ships. Then global treaties of regulations and control for ballast water and deposition from ships have been adopted. It is required to observe ballast water treatment standards (quality e.g. not containing high levels of residual agents) according to a capacity of ballast water of each ship.
As one method for it, ballast water treatment equipment (Patent Document 1; Japanese Laid-Open Patent Publication No. 2007-144391: FIG. 2) is suggested. The equipment comprises: a filtering device for water intake to the ballast tank filtering seawater to trap and remove relatively-large sized aquatic creatures such as phytoplankton, animal plankton or the like; a fungicide adding device supplying fungicide (sodium hypochlorite) to the filtered seawater (direct adding of the fungicide or making fungicide by electrolysis of seawater); a first venturi tube put in downstream of the fungicide adding device, and damaging and eliminating the aquatic creatures by diffusing the fungicide to the filtered seawater with Venturi effect; a decomposition agent supplying device decomposing the fungicide in the ballast water for draining; a second venturi tube put in downstream of the decomposition agent supplying device, and diffusing decomposition agent (one venturi tube is used as both the first and the second venturi tubes.). And the Patent Document 1 (FIG. 3) teaches that increasing fungicidal capacity by supplying more fungicide into downstream of the last venturi tube.
There are several ways to add the fungicide by electrolysis of seawater (e.g. Patent Document 2; Japanese Laid-Open Patent Publication No. 1406-254567). In ballast water treatment, it is required to treat a large amount of ballast water rapidly without concentration difference of the fungicide. Therefore, it is not suitable to add only the fungicide generated by electrolysis of seawater and to dose the generated fungicide, because such the way of treatment may not damage or eliminate some of the aquatic creatures due to the concentration difference of the fungicide. The Patent Document 1 teaches a method of constant diffusion of the fungicide by using the venture tube.
After diffusing the fungicide, the ship voyages to next wayport while keeping a constant concentration (which can inhibit bleeding of bacteria) of the fungicide. The fungicide in the ballast water is decomposed with the decomposition agent, when the ballast water is drained at the next wayport. At that time, to decompose the fungicide completely, it is required to add excess decomposition agent. Accordingly, residual decomposition agent in the ballast water brings pollution to the seawater.
In addition, a high-efficient venturi tube having a recess for generating a shear flow opening to a throat to generate micro-nano bubbles is shown in Patent Document 3 (Japanese Laid-Open Patent Publication No. 2009-136864).